Automatic exposure calibration adjustment



Nov. 30, 1965 D. w. COLEMAN 3,220,329

AUTOMATIC EXPOSURE CALIBRATION ADJUSTMENT Original Filed July 19, 1962 2Sheets-Sheet 1 Fig.

DONAL 0 W COLEMAN 1N VEN TOR BY 774M M 7PMM.

ATTORNEYS Nov. 30, 1965 p, w. COLEMAN 3,220,329

AUTOMATIC EXPOSURE CALIBRATION ADJUSTMENT Original Filed July 19, 1962 2Sheets-Sheet 2 Fig. 3

DONALD W COLEMAN INVEN TOR.

By failzw United States Patent 3,220,329 AUTOMATIC EXPOSURE CALIBRATIONADJUSTMENT Donald William Coleman, Rochester, N.Y., assignor to This isa continuation of my prior copending application Ser. No. 211,051, filedon July 19, 1962, now abandoned.

This invention relates to devices for regulating the automatic exposureof film in cameras and, more particularly, to the special calibrationand control of such devices to compensate for the personal desire of theoperator to slightly underexpose or slightly overexpose the photographsbeing taken.

What constitutes the best photograph among acceptable photographs isgenerally a matter of personal taste. This is particularly true in colorphotography, since many people prefer the more saturated colors of aslightly underexposed photograph, while others prefer the lighter hueswhich result with more exposure than normal. With cameras in which theoperator manually adjusts for exposure, it is a relatively simple matterto increase or decrease the camera aperture from the normal asdetermined by a separate light meter. However, with cameras in whichexposure control is fully automatic, the cameras exposure setting isvaried with scene brightness according to predeterminedintensity-exposure value relationships. Since these predeterminedrelationships are builtin to the camera by the manufacturer, allexposure adjustments are made to assure normal exposure. With such priorart automatic exposure control cameras, the operator cannot adjust forthis personal exposure preference.

The invention herein overcomes this problem by providing a device whichcan be easily and economically incorporated into most automatic exposurecontrol systems to permit a simple adjustment of the system by theoperator so that all automatically set exposures will reflect theoperators preference for normally exposed, underexposed, or overexposedpictures. The device is based upon a manual overdrive which may be usedto introduce a predetermined bias into the cameras meter-movementcalibration control. Such calibration controls are well known in theautomatic exposure control art, and they are generally movable memberswhose setting (usually for film speed) adjusts such devices asattenuator slides masking the cameras photocell, rheostats in serieswith the galvanometer coil, or the starting position of the entire metermovement. The manual overdrive according to the invention herein hasthree positions: normal, which retains the manufacturers calibration; aminus setting which causes all calibrated exposure values to be reducedby one-half exposure value unit; and a plus setting which causes allcalibrated exposure values to be increased by one-half exposure valueunit. By merely presetting the manual overdrive, the operator biases thecameras exposure control system to obtain the particular acceptableexposure which he prefers.

It is an object of this invention to provide a new and improved .devicefor varying the calibration of automatic control systems for cameras.

It is a further object to provide a device that will permit the cameraoperator to vary the automatic exposure control calibration of a camerato assure photographs inaccordance with the operators personal taste fornormal exposure, or slightly overexposure or slight underexposure.

It is another object to provide a simple and economical device foroverdriving the calibration control of a cameras automatic exposurecontrol system to cause the system to overexpose or underexpose by apie-selected amount.

Other objects, purposes and characteristic features of the presentinvention will be in part obvious from the accompanying drawings, and inpart pointed out as the description of the invention progresses. Indescribing the invention in detail, reference will be made to theaccompanying drawings in which like reference characters designatecorresponding parts throughout the several views, and in which:

FIG. 1 illustrates a simple movie camera incorporating the inventionherein;

FIG. 2 is a partially exploded perspective drawing of certain cameraparts pertinent to the disclosure of the invention herein; and

FIG. 3 is a plane view of the index stud, the dial face, and thecalibrated scale of film speeds as they might appear on a camerautilizing the invention herein.

Although it will be apparent that the invention herein can be integratedwith most automatic'exposure control systems and can be applied equallyto all types of cameras, the following disclosure will be limited to adescription of a single application of the invention to a simple moviecamera whose automatic exposure control system utilizes a maskedphotocell.

Referring now to FIG. 1, camera 11 is a simple movie camera of the fullyautomatic type. It has a picturetaking axis 13 on which are aligned thecameras lens system, shutter mechanism, and a variably controllableaperture. In the manner well known in the art, light from the scenebeing photographed strikes the diffusing face of photocell 15 to producea current which varies in accordance with scene brightness, and thiscurrent is used to operate a galvanometer coil which in turn controlsvanes which vary the size of the cameras aperture in accordance with thebrightness of the scene. To compensate for the various speeds ofdifferent films that may be used in the camera, the operator rotatescontrol disc 17 until indicator mark 19 aligns with the particular filmspeed on calibrated scale 21 that corresponds to the speed of the filmbeing used in the camera. The adjustment for film speed by rotation ofcontrol disc 17 causes attenuator slide or mask 23 to move into apredetermined overlapping relation with photocell 15, assuring that, forany given scene brightness, greater exposure will be provided for slowerspeed films. When camera 11 has been set for normal operation, itoperates similar to other prior art cameras of this general type,namely, the operator merely directs the camera at the scene to bephotographed, depresses film drive control knob 25 and the camerasexposure system automatically provides the proper normal exposure of thefilm for the varying conditions of brightness in the scenes beingphotographed.

Referring now to the partially exploded perspective of FIG. 2,attenuator slide 23 is shown controlled by lever arm 27 which ispivotally mounted on pin 28 of control disc 17 and which engages pivot29 with slot 31 and pin 33 of attenuator slide 23 with slot 35. Ascontrol disc 17 is rotated in a counterclockwise direction, the movementof lever arm 27 causes attenuator slide 23 .to move up between guides 37to mask photocell 15 in Dial face 55 which carries calibrated scale 21,is illustrated as being separate from overdrive ring 49, but this hasbeen done merely to facilitate explanation of the device; in actualpractice dial face 55 would be secured to, or be part of the same unitas, overdrive ring 49.

Overdrive ring 49 has extending therefrom a finger 57 on which ismounted index stud 59. Index stud 59 is designed to cooperate with holes61, 62 and 63 in locking plate 64 which is secured to the camera body bymeans of screw 65.

A spring 67 is axially mounted on shaftlike extention 69 of indicatormember 41 and serves to bias the dial assembly, including overdrive ring49 and dial face 55 in an axial direction tending to hold index stud 59engaged to one of the holes 61, 62 and 63 in locking plate 64.

Locking plate 64 has its three holes 61, 62 and 63 marked N, and andcalibrated scale 21 on the face of dial face 55 carries index mark 71which is aligned with one of the three just-named symbols in accordancewith the particular hole in which index stud 59 is engaged.

The operation of this device is as follows: Referring to FIG. 3, uponloading film in the camera the operator rotates control disc 17 untilindicator mark 19 is aligned with the particular number on calibratedscale 21 which corresponds to the speed of the film which has beenloaded into the camera. The setting of control disc 17 occurs withoutthe concurrent motion of overdrive ring 49 which is held in position byvirtue of the engagement of index stud 59 with hole 62. During thesetting of control disc 17, protrusion 43 is moved to another slot 47,the movement of control ring 17 overcoming the resilient bias ofindicator member 41.

If the operator prefers that his photographs be made with normalexposure, he leaves the calibration unit in a position as illustrated inFIG. 3, namely, with index stud 59 in center hole 62 of locking plate64, as indicated by the alignment of index mark 71 with the letter N37However, should the operator prefer photographs which result from aslight underexposure, he can preset the calibration unit to provide suchuniform underexposure by merely depressing dial face 55 against theinfiuence of spring 67 until index stud 59 disengages center hole 62.Then, holding the dial face in this depressed condition, he rotates itclockwise until index stud 59 is in alignment with lefthand hole 61 oflocking plate 64, as will be indicated by the alignment of index mark 71with the symbol The distances between holes 61, 62 and 63 in lockingplate 64 are preselected to require the rotation of control disc 17through an arc equivalent to one-half an exposure value unit. Therefore,the clockwise rotation of the entire calibration unit as just described,causes control disc 17 to move so that attenuator slide 23 moves out ofmasking relation to photocell 15 in an amount equivalent to one-half anexposure value unit. As the result of this, for any given scenebrightness, photocell 15 puts out a greater current, causing greaterrotation of the galvanometer coil, and thereby resulting in a smalleraperture in a manner well known in the art.

Similarly, should the operator prefer his photographs taken underslightly overexposed conditions, he depresses dial face 55 and rotatesthe entire calibration unit in a counterclockwise direction until indexstud 59 is aligned with righthand hole 63, as indicated by the alignmentof index mark 71 with the symbol This counterclockwise motion of theentire calibration unit including control disc 17 causes attenuatorslide 23 to move to a position masking more of the surface area ofphotocell 15, thereby causing the automatic exposure control mechanismto respond with an aperture which is predetermined to result in anoverexposure equivalent to onehalf an exposure value unit.

Thus, by this relatively simple device, the camera operator canoverdrive the cameras automatic exposure control system in accordancewith his preference for normal exposures, underexposures, oroverexposures. The setting of the camera is extremely simple from theoperators point of view, and the desired variation in exposure isautomatically calibrated for all conditions of scene illumination.

It should be understood that only one specific embodiment of the presentinvention has been described herein, and that the particular formdisclosed has been selected to facilitate the disclosure of theinvention rather than to limit the particular form which the inventionmay assume. Further, it should be understood that various modifications,adaptations, and alterations may be applied to the specific form shownto meet various requirements of practice without in any manner departingfrom the spirit or the scope of the present invention.

Iclaim:

1. In a camera having a picture-taking axis and an automatic exposurecontrol system for varying the light passing along said axis inaccordance with scene brightness, said system including a calibratedcontrol member movable to predetermined positions for manually adjustingthe light intensity-exposure value response of said system in accordancewith known variables to provide normal exposure of film used in saidcamera, the improvement comprising: overdrive means coupled to saidcontrol member and movable from a first position to either of a secondposition or a third position for driving said control member to aposition altering the light intensity-exposure value response of saidsystem by one-half exposure value unit above and below, respectively,the preselected normal exposure response as determined by an initialsetting of said control member, the alteration causing a slightovergrlrposure and slight underexposure, respectively, of said 2. In acamera having a picture-taking axis and an automatic exposure controlsystem for varying the light passing along said axis in accordance withscene brightness, said system including a calibrated control membermovable to predetermined positions for manually adjusting the lightintensity-exposure value response of said system in accordance withknown variables to provide normal exposure of film used in said camera,the improvement comprising: overdrive means coupled to said controlmember and movable from a first position to either a second position ora third position for driving said control member to a position alteringthe light intensity-exposure value response of said system by apredetermined amount above and below, respectively, the preselectednormal exposure response as determined by an initial setting of saidcontrol member, the alteration being of such magnitude to cause apredetermined slight overexposure and slight underexposure,respectively, of said film, said overdrive means comprising: anadjustable overdrive member movable from said first position to eithersaid second or said third position, resilient means connecting saidoverdrive member to said control member, spring means, an index studfixed to said overdrive member; locking means for maintaining saidoverdrive member in any one of said first, second, and third positions,said locking means comprising a stationary plate having defined thereinat least three apertures corresponding to said first, second and thirdpositions, the apertures being provided for receiving said stud, saidoverdrive member being biased against said plate by said spring means,whereby said control member is movable with said overdrive member whenthe position of said overdrive member is changed.

3. In a camera having a picture-taking axis and an automatic exposurecontrol system for varying the light passing along said axis inaccordance with scene brightness, said system including a calibratedcontrol member movable to predetermined positions for manually adjustingthe light intensity-exposure value response of said system in accordancewith known variables to provide normal exposure of film used in saidcamera, the improvement comprising: overdrive means coupled to saidcontrol member and movable from a first position to either of apredetermined second position or a predetermined third position fordriving said control member to a position altering the lightintensity-exposure value response of said system by less than oneexposure value unit above and below, respectively, said preselectednormal exposure response as determined by an initial setting of saidcontrol member, the alteration being of such magnitude to cause apredetermined slight overexposure and slight underexposure,respectively, of said film.

4. The camera according to claim 3 wherein said overdrive meanscomprises: an adjustable overdrive member movable from a first positionto either of a second position and a third position, resilient meansconnecting said overdrive member to said control member; and lockingmeans for maintaining said overdrive member in any one of said first,second and third positions following movement thereto; said controlmember being movable against said resilient means when said overdrivemember is held immobile by said locking means, and said control membermoving with said overdrive member when the position of said overdrivemember is changed.

References Cited by the Examiner UNITED STATES PATENTS 3/1961 Ort 95-644/1963 Akahane 95-64 X

1. IN A CAMERA HAVING A PICTURE-TAKING AXIS AND AN AUTOMATIC EXPOSURECONTROL SYSTEM FOR VARYING THE LIGHT PASSING ALONG SAID AXIS INACCORDANCE WITH SCENE BRIGHTNESS, SAID SYSTEM INCLUDING A CALIBRATEDCONTROL MEMBER MOVABLE TO PREDETERMINED POSITIONS FOR MANUALLY ADJUSTINGTHE LIGHT INTENSITY-EXPOSURE VALUE RESPONSE OF SAID SYSTEM IN ACCORDANCEWITH KNOWN VARIABLES TO PROVIDE NORMAL EXPOSURE OF FILM USED IN SAIDCAMERA, THE IMPROVEMENT COMPRISING: OVERDRIVE MEANS COUPLED TO SAIDCONTROL MEMBER AND MOVABLE FROM A FIRST POSITION TO EITHER OF A